Longitudinally adjustable gas springs are basically known from U.S. Pat. No. 3,656,593 and are very well known through their wide usage. A basic problem of these longitudinally adjustable gas springs has resided in the fact that a large number of seals are required which have to be disposed between the plug and the respective inner wall of the outer tube, the body of the valve and the respective inner wall of the outer tube and the body of the valve and the inner tube. As a rule, additional seals are disposed between the piston rod and the piston. Problems are caused in two ways by the use of such seals, because on the one hand respective parts have to be cut for grooves to receive the annular seals, which requires machining; on the other hand the danger exists that seals might be damaged during installation, which would completely ruin the lengthwise adjustable spring. A particular problem is that small defects often mean that the damage is only apparent after some time, after the gas spring has already left the factory and has been installed on the job. This danger could in the past only be avoided in reality by a mostly manual installation process.
A basically similar longitudinally adjustable gas spring is known from DE-PS 22 25 342, the valve body of which is disposed conically tapered. The outer tube of the gas spring is pressed against this valve body in order to form a conical part of the housing, which can be employed as a tapered cone.
Furthermore, copending U.S. Ser. No. 114,652, now U.S. Pat. No. 4,318,536, describes a longitudinally adjustable gas spring of this same general type, which is equipped additionally with a so-called limit suspension. Here, on the one hand a locking element is combined with the piston, and on the other hand a valve area limiting sleeve is disposed on the side towards the valve.